During the First World War, the battle at sea was mainly characterised by large-scale use of submarines. When the German empire lost the arms race for the largest fleet against Great Britain and the British blockade prevented the German battle fleet from leaving port, the importance of German submarines increased. The technology was still very primitive and was not yet used to its full extent during the war, but the importance of this new weapon soon became clear.
The U-boats were especially active in the Mediterranean and the seas surrounding Great Britain and Ireland. They sowed panic and sunk numerous vessels which were vital in transporting troops and supplies. The ports of Ostend, Zeebrugge and Bruges, the only ports which the Germans managed to conquer, played an important role in the North Sea and the English Channel. The Marinekorps Flandern, which set sail from these ports under the command of Ludwig von Schröder, was responsible for sinking one third of the total Allied tonnage sunk. These ports and the coast were protected by a coastal defence line consisting of 35 batteries, including the Aachen battery.
The submarine attacks not only resulted in the entry of the United States in the war, but were also the reason behind the battle of Passchendaele in 1917 (the aim of this operation was to conquer the ports of Ostend and Zeebrugge). When this battle did not produce the desired effect, the Allies launched an equally unsuccessful raid on Zeebrugge and Ostend in 1918.
The German submarines nevertheless lost in strength by the end of the war due to exhaustion of German raw materials but also because of British measures such as the introduction of convoys and the laying of mines and nets in the Channel.